1. Field of the Invention
This invention relates to an engaging member of a surface fastener made of thermoplastic synthetic resin and comprising a flat substrate sheet and a large number of engaging elements injection molded integrally, more particularly, it relates to a molded engaging member of a surface fastener adapted to have a desired engaging rate, an adequate level of peeling resistance and an enhanced degree of engaging strength when used with a piece of pile product having long piles such as a carpet or some other interior decoration.
2. Description of the Related Art
In recent years, surface fasteners comprising a flat substrate sheet and a large number of male engaging elements made of a synthetic resin material and molded integrally with each other provide a wide range of applications including holders to be used with sanitary goods such as paper nappies, interior decorations, bedding articles, various sheet covers and even grind stones. The male engaging elements arranged on a flat substrate sheet may have an anchor shape or mushroom shape or show some other profile adapted to operate as hooks.
A molded engaging member of a surface fastener of the above identified type may be somewhat less flexible if compared with a conventional engaging member of a surface fastener made of woven fabric but each of its engaging elements provides greater engaging strength with loops of a companion woven surface fastener. Thus, such engaging members find ever-increasing applications including those listed above and also as holders for securely holding various industrial articles. The male engaging member of a surface fastener to be used for holding a carpet or an interior article of a motor vehicle will have to be made to show relatively large dimensions in order to have a desired degree of engaging strength, which inevitably reduces the number of hooks arranged per unit surface area (the density of engaging elements) and hence the rate of engagement of the hooks with the loops on a matching engaging member to be coupled with it is lowered. Then, in order to secure the desired engaging strength, the hooked free end of each engaging element is required to have a certain level of rigidity.
With the known molded engaging member of a surface fastener, the hooks arranged on the male engaging member are pressed by an engaging surface of a female engaging member when they are coupled with each other in such a way that the sides carrying the respective engaging elements are made to face each other. Then, as a result, the small hooks are bent either frontward or sideways to consequently close the hooks and the loops of the female engaging member are mostly forced to become flat and less apt to be caught by the hooks. Additionally, the peeling resistance of such an engaging member depends mostly on the rigidity of the hooks and hence will be reduced when the hooks are made to be highly flexible.
Thus, with known molded surface fasteners, there has been a tradeoff between the rigidity of the material and the flexibility of the fastener. If the surface fastener is molded of a highly rigid material, the engaging strength of the surface fastener will be too strong to damage the male and female engaging members when they are peeled off from each other. If, on the other hand, the surface fastener is made of a highly flexible material, engaging portions can easily be deformed and become disengaged to unintendedly separate the male and female engaging members of the fastener. Therefore, they are not adapted for holders to be used with industrial articles and interior decorations that are required to have an adequate level of engaging strength and peeling resistance.
Particularly, if the companion female engaging member is a carpet having long piles, the piles are longer than the hooks so that the hooks cannot get to the base portions of the piles and will tend to drift when engaged with corresponding piles at a top or middle portion thereof. Then, the drifting hooks engaged with the corresponding long piles only at a top or middle portion thereof can easily become disengaged when they collide with each other and hence cannot operate stably as holders.
If, similarly, the known male engaging member is pressed against a carpet having a mixture of long and short piles standing therefrom, the hooks of the engaging member having an ordinary height cannot reach the surface of the substrate sheet nor engage with the short piles as they are blocked by the long piles. If some of the hooks are successfully engaged with the short piles, they are constantly urged upward by the long piles surrounding them so that they are incessantly pulled and apt to become degraded and the short piles held by them tend to be cut by the pulling force to eventually damage the carpet. The above described situation will be applicable not only to hooks but also to engaging elements that are mushroom-shaped and those having some other profile.
Various engaging members of surface fastener have been proposed to bypass the above described drawbacks of conventional surface fasteners, particularly that of the dimensional difference between the male engaging elements of a surface fastener and the companion piles. Japanese Patent Application Laid-Open No. 8-19406 discloses such an engaging member of a surface fastener comprising a large number of identical male engaging elements arranged on a flat substrate sheet and molded integrally with it. Each of the male engaging elements have a stem rising upright from the substrate sheet, a hook-shaped engaging portion arcuately extending from part of the upper end of the stem and a branch portion extending from the remaining portion of the upper end of the stem to rise higher than the hook-shaped engaging portion to a predetermined extent and having a curved tip directed oppositely relative to the hook-shaped engaging portion, the engaging element additionally having reinforcement ribs arranged on the lateral sides of the stem.
When the engaging surface of the proposed male engaging member of a surface fastener is placed on and pressed against the engaging surface of a female engaging member to be coupled with it, the curved tips of the branch portions are pushed against the engaging surface of the female engaging member. Under this condition, the branch portion of each male engaging element is moved into the long piles of the female engaging member and eventually abuts the surface of the substrate sheet thereof to force the curved tip to bend downward and also the branch main body and the stem to turn downward around the base of the stem. As a result, the hook-shaped engaging portion arcuately extending from the stem and directed oppositely relative to the branch portion is also turned and deformed accordingly to enlarge the gap between the front end of the hook and the hook main body so that the hook can easily catch piles. At the same time, the curved tip of the branch portion slides on the engaging surface of the female engaging member so that piles are moved into the gap of the hook-shaped engaging portion and caught by the latter, while the curved tip of the branch portion is pushed into other piles.
To separate the thus coupled male and female engaging members, the female engaging member is pulled away from the male engaging member in a peeling direction. Then, the piles caught by each hook-shaped engaging portion are also pulled away with the female engaging member to turn the tip of the hook-shaped engaging portion upward. At the same time, the piles surrounding the curved tip of the branch section come to be engaged with the latter so that the piles located in front and at the back of the engaging element become in engagement with it to pull both the hook-shaped engaging portion and the curved tip of the branch portion upward to keep the stem in the upright position. Thus, the branch portion shows an effect of suppressing the bending tendency of the hook-shaped engaging portion to increase the engaging strength of the latter with regard to the piles caught by it.
The male engaging member disclosed in the above cited publication comprises for each engaging element a single stem rising substantially upright from the substrate sheet, a hook-shaped engaging portion arcuately extending from part of the upper end of the stem and a branch portion extending from the remaining portion of the upper end of the stem to rise higher than the hook-shaped engaging portion and having a curved tip directed oppositely relative to the hook-shaped engaging portion. The above described configuration of an engaging member is accompanied by the following drawbacks. Firstly, since the hook-shaped engaging portion and the branch portion share a common stem in each engaging element, the gaps of the hook-shaped engaging portions are enlarged to unintendedly release the piles of the female engaging member that have been caught by them when the coupled male and female engaging members are pressed against each other to depress and deform the branch portions.
Secondly, if the male engaging member is coupled with a female engaging member of such as a carpet so that the hook-shaped engaging portions and the branch portions brought into engagement with piles having uneven lengths, the turned and deformed hook-shaped engaging portions easily come to be engaged with short piles, and when the female engaging member is raised by the long piles standing densely, the piles engaged with the hook-shaped engaging portions are pulled by the resilient force of the branch portions trying to restore the original profile. As a result, the hook-shaped engaging sections are pulled up by the piles to become disengaged and/or damaged.
In short, these problems are caused by the fact that the male engaging member as disclosed in the above cited publication comprises for each male engaging element the hook-shaped engaging portion and the branch portion taller than the hook-shaped engaging portion extending from the common stem.
In view of the above identified problems, it is therefore the object of the present invention to provide an engaging member of a surface fastener comprising novel engaging elements that are flexible to a certain extent and at the same time, ensure a certain level of peeling resistance, and durable for repeated use. The engaging elements of an engaging member according to the invention can come evenly in engagement with long or various length of piles of a female engaging member such as a carpet and their hook-shaped engaging portions are not subjected to irregular and extreme force so that they may stably remain in engagement without unintentionally becoming disengaged from the companion piles.